1. Field of the Invention
This invention relates to central processing units which perform arithmetic operations in real time, and more particularly to those units which operate on real time analog signals.
2. Description of Prior Art
The techniques of digital processing of analog signals are being used in many new applications as microprocessors are becoming less expensive. These applications currently range form the filtering of audio signals to the control of heavy machinery.
A state of the art system which performs this processing is shown in FIG. 1. This system operates as follows.
The analog signal is, first, sampled, and the value is converted to a binary number. This function is performed by the binary analog to digital converter.
A computation is, next, performed on the binary number which represents the signal value. This computation typically involves a difference equation. In a difference equation, the current signal value, along with several previous signal values, are multiplied by constants, and the products are added together.
The sum is, then, converted to an analog voltage level, and is output as an analog signal. This function is performed by the binary digital to analog converter.
The problem with the state of the art systems is that many arithmetic operations are required to perform the computation.
For example, a product of two four bit binary numbers requires sixteen bit wise multiplications, six shifts, and twenty-one bit wise additions with carry. This single product would, therefore, require forty-three arithmetic operations. Each operation requires processor time, so the through put is slow.
Many state of the art systems use multiple processors to attempt to solve the problem of slow through put. The use of multiple processors, however, requires that a processor be used as a resource manager. The resource manager must communicate with, and control, the other processors, and this, in turn, slows the through put.
Objects and Advantages
In this patent application, a digital signal processing system is proposed which has faster through put. The proposed system utilizes the base four numbering system instead of the binary numbering system. This system, FIG. 2, functions as follows.
The analog signal is, first, sampled, and the value is encoded as an eight digit base four number. A base four computation is, next, performed on this number. The result is, then, converted back to an analog voltage level, and is output as an analog signal. This system has the following advantages.
The first advantage is that fewer arithmetic operations are required to perform an equivalent computation. A product of two digit base four numbers, for example, would require four digit wise multiplications, one shift, and three additions with carry. This is a total of eight arithmetic operations. This computation is equivalent to a product of two four bit binary numbers, and such a computation would require forty-three arithmetic operations, as previously discussed.
The next advantage is that a base four number can be multiplied or divided by four by a single left or right shift operation, respectively. A binary number would require two shift operations to be multiplied or divided by four. A base four number can, however, be multiplied or divided by two if the number is first converted to binary, by hardware, and then shifted.
Another advantage of a base four system is that a program branch can go one of four different ways. A program branch in a binary system can only go one of two ways. A program, in a base four system, would, therefore, require fewer steps to make decisions.
The final advantage of base four is that fewer control lines and bus lines are required, than are required by an equivalent binary system, since each line carries more information.
A base four system can, therefore, perform the same functions as a state of the art system, but requires fewer operations, since a base four system operates on larger pieces of information. A base four system, therefore, has better through put than a state of the art system.